Saturday, December 24, 2011

South-west Endemics Part 2: White-breasted Robin

The White-breasted Robin (Eopsaltria georgiana) is a characteristic resident of tangled gullies and thick understorey in the karri and jarrah forests of south-west WA, though there is also a lesser-known relict population in coastal gully thickets north of Perth. “A quietly garbed but attractive bird” was Serventy and Whittell’s description [1], capturing surprise that a grey and white robin should be so much more striking than a plumage description would make it sound.

White-breasted Robin Eopsaltria georgiana

“Peculiar” was Leach’s more prosaic assessment [2]. Taxonomy of the White-breasted Robin has been surprisingly controversial, given that to superficial appearances it seems a typical (if colourless) Eopsaltria robin. It shares many mannerisms with the Eastern and Western Yellow Robins, such as the habit of clinging sideways to low trunks and branches, motionless except for occasional flicking of the tail and wings. Like them it is initially shy but hopelessly inquisitive, and cannot resist checking you out if you sit still for a moment. Indeed it is so similar to the Yellow Robins that this complex has long been considered a classic example of speciation by double invasion, with successive waves into the south-west forests evolving to lose all (White-breasted Robin) or half (Western Yellow Robin) of an originally fully yellow breast (Eastern Yellow Robin).

However it has sufficient differences from the Yellow Robins, particularly its eggs, to persistently trouble taxonomists. Campbell first removed it from Eopsaltria to Amaurodryas (now Melanodryas) based on a perceived “oological” association with the Dusky Robin of Tasmania; Mathews lumped it instead with Mangrove Robin in the genus Quoyornis, where it remained isolated for some time after Mangrove Robin was split off to yet another monospecific genus Peneonanthe [2]. However a 2009 molecular phylogenetic study [3] reported the unexpected finding that the White-breasted Robin may instead be most closely related to the ‘other’ yellow robins - the two Tregellasia robins (the White-faced and Pale Yellow Robin of north-eastern rainforests).
UPDATE: Christidis et al 2011 [6] confimed this unexpected paraphyletic status of Eopsaltria and recommended that White-breasted Robin return to the genus Quoyornis.

Typical pose for a White-breasted Robin - sideways on a low branch, eyeballing an intruder into its territory

This is a surprising result (and needs further confirmation UPDATE - now confirmed by Christidis et al 2011 [6]), but fits with at least one unusual aspect of its biology – the habit of cooperative breeding (also seen in the Tregellasia robins). For example, a 2004 study in karri forest near Manjimup [4] found that 2/3rds of all breeding pairs had one or more ‘helpers’, predominantly junior males, helping to feed the brooding female and young. This reproductive strategy is successful as part of a ‘slow’ life history, with only a small crop of yearlings annually but a high survival of adults sedentary on high quality territories.

There are no subspecies described, though Ford thought the northern population had a unique call and a slightly lighter, more blue-grey colour dorsally [5]. That this population was only discovered in 1957 is surprising, given that it extends all the way from Geraldton to Perth.  This population seems to have abandoned the preference for freshwater typical of southern birds (which prefer thickets fringing creeks or swamps) and is instead found in dense wattle and melaleuca thickets close to the coast, though there are a few pockets further inland such as at Lake Indoon near Eneabba.

Where to see White-breasted Robin:
This endemic species is perhaps easiest to find in karri forest, where it is particularly associated with thickets of Karri Hazel (Trymalium spathulatum). However in the southern parts of its range (including the Cape-to-Cape region) it can be found in any area of dense vegetation, including coastal peppermint (Agonis) scrub. In Darling Range jarrah forest, it is more typically confined to thick creek-side vegetation of the deeper and wetter gullies. Close to Perth, the Calothamnus thickets at the base of Victoria Reservoir wall are a particularly reliable site, as is Wungong gorge. The northern population also extends (sparsely) into suburban Perth at sites such as the coastal path south of the Ocean Reef boat ramp. However White-breasted Robin can turn up in suitable vegetation anywhere within its range, as illustrated by occasional records from Dryandra, and the isolated populations on Bald and Michaelmas Islands.

Given its shyness and preference for thick vegetation, locating White-breasted Robin is much easier if you learn its clipped “tchek tchek” alarm call – its full song is rarely heard.

White-breasted Robin at Victoria Reservoir near Perth

[1] Serventy DL & Whittell HM (1976). Birds of Western Australia. Perth: University of Western Australia Press.
[2] Whittell HM (1932). Notes on the White-breasted Robin. Emu 32(4): 236-240
[3] Loynes K, Joseph P, Keogh JS (2009). Multi-locus phylogeny clarifies the systematics of the Australo-Papuan robins (Family Petrocidae, Passerfomes). Molecular Phylogenetics and Evolution 53: 212-219.
[4] Russell Em, Brown RJ, Brown MN. Life history of the White-breasted Robin, Eopsaltria Georgiana (Petroicidae), in south-western Australia. Aust J Zool 2004; 52(2):111-145
[5] Ford JR & Teague BV (1959). Extension of range in the White-breasted Robin. Emu 59: 37-39
[6] Christidis L et al. Mitochondrial and nuclear DNA phylogenies reveal a complex evolutionary history in the Australasian robins (Passeriformes: Petroicidae). Molecular Phylogenetics and Evolution 2011; 61: 726-738

Sorry - couldn't resist this 'endemic' take on the traditional robin Christmas card!

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